Vasopressin acts on which receptors to cause vasoconstriction and increase water reabsorption?

• A. V1 only
• B. V1, V2, V3 receptors
• C. V2 only
• D. V3 only

Answer: (B)

Vasopressin works through different receptor subtypes in multiple tissues, each mediating distinct effects. The vasoconstrictor action comes from V1 receptors on vascular smooth muscle; when activated, they trigger a signaling cascade that increases calcium and causes contraction, raising vascular tone. The antidiuretic effect comes from V2 receptors in the kidney’s collecting ducts; they stimulate a cAMP pathway that promotes insertion of aquaporin-2 water channels, increasing water reabsorption. V3 receptors, primarily in the pituitary, stimulate ACTH release, adding a hormonal regulatory layer that can influence systemic responses to vasopressin. Because vasopressin exerts its effects via all three receptor types, the best answer includes V1, V2, and V3.